Antioffset composition



, faces.

of the desired lands.

Patented Au -1, 1944 2,354,979 ANTIOFFSET coMrosrrIoN Ernest G. Alm'y,Tamaqua, Pa., assignor to Atlas Powder Company, Wilmington, DeL, acorporation of Delaware No Drawing. Application April 15,1942,

Serial No. 439,107

Claims.

the sheet next to it. A number of methods have been devised to eliminateor minimize offset. One procedure has beento protect the ink film byspraying the sheets after printing with an anti-offsetting medium whichdeposits -lands or projections higher .than the ink film on the printedsheet to protect it from adjacent sur- Such a method .is that describedin U. S. Patent No. 2,078,790, issued April 27, 1937, to Edmond H. Bucy.This patent teaches employing an anti-ofiset medium which comprises aland-forming ingredient contained in an evaporable solvent. Theanti-offset, composition is sprayed onto the sheets in such manner thatthe solvent volatilizes as the droplets travel to the sheet, producingsmall, dried or partially dried,

particles which adhere to the sheet in the form Another anti-onsetmethod Bucy Patent No. 2,142,666, issued January 3, 1939. According tothis method, the inked surface is contacted with a roller, the surfaceof which contains numerous, small depressions or pits holdinganti-ofiset composition. Composition deposits from the roller onto theinkedsurface to form the lands. Thepits in the roller are then refilledwith anti-offset composition for further application. This methodparticularly adapted for preventing offset on work from web-fed presses.

- A number of compositions have been devised which are useful in theBucy processes. "Two, which are the subject matter of Bucy Patents Nos.2,111 2,667 and 2,142,668, issued January 3, 1939, employ land-formingmaterials such as cellulose esters .or ethers and two solvents, one morereadily volatile than the other.

It is an object of the present invention to provide for the preventionof offset by the application of new anti-offset processes andcompositions.

It s further among the objects of the invention 0 provide anti-offsetcompositions which are economical to use and readily-applied.

Often, and especially in multicolor work, each sheet is separatelyprinted a number of times. Some prior art anti-offset compositions,while adequately effective for preventing ofiset, have shown a tendencyto be picked up from the treated surface when a second impression ismade.

is described in The picked-up composition deposits in with the rest ofthe raised surfaces. An undesirable blurred print results. Some ofisetcompositions on drying have also caused abrasion to printing equipment,limiting. the life of rolls in presses through which printed matter maysubsequently pass. Another object of the present invention is theproduction of anti-offset compositions which will have improvedcharacteristics of pick-up and abrasion on presses.

Other objects will be apparent from the following descriptiorn It hasbeen found that solutions of combinations of a soluble organiccompoundcontaining at least 3- hydroxyl groups, a boric-acid producingmaterial, and alkali are excellent anti-oifset compositions.

The soluble organic compounds containing at least 3 hydroxyl groupsusable for'this invention preferably are ones containing a chain ofnomore than 6 carbon atoms. are the polyhydric compounds, glycerol,erythritol, pentitols, pentoses, hexitols and hexoses.

As alkalies can be used any of the alkalies containing an alkali metal,ammonia, or watersoluble amines, such as triethanolamine. By alka1ies asused irrthis specification are meant those containing akali metal,ammonium or water-soluble amine radicals.

As a boric-acid producing material can be used any boron compound whichforms orthoborlc acid, HsBOa in solution, such as metaboric acid, HBOz,tetraboric acid, HzB-iOv, or boron trio zide, B203. Both alkali andboric-acid producing material may be, at least in part, simultaneouslyprovided by borate salts of the alkalies,- as, for

example, borax.

An anti-offset composition of the, present invention may be readilyprepared by dissolving the separate ingredients in water. Whether or nota reaction occurs amongst the ingredients so-dissolved is at present notknown. If hydroxy-containing organic compounds of the typehereinemployed and boric 'acid are heated together so as to drive off water,organic borate resins are formed which contain-a borm acid moleculecondensed with the hydroxyl-containing organic compound molecule: Forexample,.

sorbitol monoborate dicondensation product may be formed from thereaction of 1 mol of boric acid and 1 mol of sorbitol. Each boron atomin the resin contains a residual acid hydroxyl group which may bereacted with alkali with the resultant formation of alkali sorbitolborate. The reactions of boric acid with the other hydroxylcontainingorganic compounds of the type used Examples of such and the alkali aredissolved separately in water or whether combined forms of theseingredients are dissolved in water. For example, employing sorbitol asexemplary of the hydroxyl-containing organic compound, the combinationof this invention may be prepared by dissolving sorbitol,- alkaliand'boric acid in water separately; it may also be prepared bydissolving alkali sorbitol borate in water; it may be 'further'preparedby dissolving sorbitol borate and alkali in water: or again it may beprepared by dissolving sorbitol and an alkali borate, such as borax, inwater.

It is usually preferred to employ the organic compound containing atleast 3 hydroxyl groups and the boric acid material in proportions suchthat they will be approximatelyone atom of boron for each molecule oforganic compound. These proportions are not' highly critical, butsometimes, if too little boric acid material is employed, the excessorganic compound will plasticize the lands, making them too soft. On theother hand, too much boric acid material may result in a crystallizingout of boric acid from the solution before it is applied.

The properties of these new anti-offset compositions difier somewhatdepending upon the particular organic compounds employed. Hardness ofthe lands and their efllciencyas an antiofiset medium appears toincrease, in general, with the number of hydroxy groups and chainedcarbon atom-s in the organic material used. Glycol compositions are toosoft for much commercial use. Glycerine compositions are harder and canbe used if sufficiently concentrated. Hexitols, particularly sorbitolcompositions, apparently produce the most workable solutions. Hexosecompositions, for example, glucose, have the advantage of very low cost,but solutions prepared with hexoses are not as stable to standing as arethe hexitols. Because of their cheapness, however, they have manyanti-offset applications.

Control of the amount of alkali present in the composition efiects to aconsiderable degree regulation of the Properties of the lands. Afterhydroxyl-containing organic compounds have been reacted with boric acidto produce borate resins, each atom 'of boronhas still attached to it anacid hydrogen "atom which may be reacted with one equivalent of alkali.The resin exhibits properties of increased viscosity and hardness as thealkali content increases toward complete satisfaction of all moleculescontaining an acid group. Similar properties of increased hardness maybe noticed in the lands produced from anti-offset solutions of thisinvention when they are prepared with increased concentrations ofalkali. This effect is apparently-related'to the property of the alkaliof making the drops crust over on evaporation. This is desirable becausethe droplets appear to be dry on their surfaces and less permanently tothe paper so that a permanently rough surface need not be produced. The

.ability to change the character and particularly the hardness of thelands by variation in the alkali content or pH of the anti-offsetsolution is an important advantage of this invention, for it provides aneasy method of suiting the lands to the particular job in-hand.Preferably, the

2,354,979 compound, the boric acid producing material,

mately 0.5 to 1 gram equivalent of alkali per gram atom of boronpresent. A solution containing 0.5 equivalent of sodium per atomicweight of boron is conveniently made by adding borax (Na2B4O'1 in whichthe ratio of sodium to boron is 0.5) to a solution ofhydroxyl-containing organic compound of the type employed in thisinvention. For example, if 1 mol of sorbitol and 0.25 mol of borax areadded to water, a solution is obtained equivalent to that where a 0.5alkali reacted sorbitol borate is dissolved in water. It is usuallypreferable not to employ more than one equivalent of alkali per gramatom of boron because the lands become over-brittle and excess alkalimay harm some papers. Below a 0.5 equivalent of alkali per atomic weightof boron, the skin-forming effect is largely lost. For some work asolution corresponding to a sorbitol borate reacted with 0.95equivalents of alkali per. mol of borate has been found ideal. Asindicated above, however, the alkali content should be adjusted for theparticular job to be performed.

The proportion of solids in the solution is not at all critical but willdepend largely on the type of printing for which the solution isprepared. Also it depends greatly on the particular organic compoundemployed. Glycerine requires more concentrated solutions than do thehexitols. Thus work using heavy inks on coarse papers generally requireslarger lands than does finer work. Usually, more concentrated solutionsare more viscous and will give larger lands than those of lessconcentration. Forv spraying purposes it has been found that lessconcentrated solutions are generally required than for the roll process.

A low boiling solvent more volatile than water such as, for example,dioxane, acetone, or watermiscible alcohols such as methyl, ethyl, orisopropyl alcohol, is conveniently added to antioffset compositions ofthis invention as a drying aid.

It has been found that the spraying properties of these anti-offsetsolutions may be improved very appreciably by the addition of smallproportions of an agent which is compatible with the solution and whichexhibits gelatinizing tendencies therewith. Some gums have been foundsuitable for this purpose. Gum karaya, gum arabic, and locust gum arepreferred examples of these. Other materials which may be employed arepolyvinyl alcohol and starch acetate in their water-dispersiblemodifications. The improvement effected by these gelatinizing agents isa lessening of the proportion of total solids necessary to provide ausable composition. When one of them is present, a less concentratedsolution is substantially equivalent to a more concentrated, and,hence,-more expensive solution prepared without a gelatinizing agent.The reasons for this are not fully understood, but, without anyintention to limit the invention to the correctness of the explanation,it is suggested that the action of the gelatinizing substance is twofold. The viscosity of the solution is increased moderately, and thesolution becomes stringy, exhibiting an increased property ofcohesiveness. Both of these efiects, and particularly the latter, makefor coarser atomization from the spray gun, so that the average particlesize of the spray is larger and less of the solution is wasted informing fines which do not produce the desired lands.

solutions of this invention contain from approxi- The anti-offsetcomposition of the invention may also contain inert ingredientscontained in other anti-offset ciunpositions providing they areoperative therewith. A few examples of ingredients to improve them.

viously prepared solution of gum karaya in the such ingredients are:organic soaps. such as aluminum stearate. aluminum palmitate, r zincstearate, or materialssuch as asbestine, diatomaceous earth, fullersearth, magnesium carbonate, talc, powdered mica, powdered magnesium,powdered aluminum hydrate, a starch such as corn starch, etc.Furthermore, the compo.-

sitions of this invention may be added to other anti-ofiset compositionscontaining such or other The solutions of thisinvention may applied inany convenient manner. Spray and roller techniques are known in the art.It is Example 1- An anti-oil'set solution was prepared with thefollowing ingredients:

Percent by weight Sodium sorbitol borate 33.3 95% ethyl alcohol 11.1Water 55.6

The borate was prepared by heating equimolar 1 parts of anon-crystallizing sorbitol of the type disclosed in U. S. Patent No.2,172,357, issued September 12, 1939, to K. R. Brown, thoughcryscomposition. This solution when applied in the usual manner wasfound to be excellent in producing lands which eliminated oflset withoutperceptible roughening of the, surface, and also did not show thepick-up and abrasive properties characteristics of some prior artsolutions. The solution. also showed no tendency to clog 'up sprayingequipment.

Example 2 This example shows how the addition of a small quantity of agum such as gum karaya will permit the use of lesser solidsconcentration.

A solution of the following composition exhibited much the same sprayingproperties as did the solution of Example 1.

Percent by weight Sodium sorbitol borate 20 95% ethyl alcohol 10 Gumkaraya 0.1 Water 72.9

'in Example 1. It was diluted with one-third its weight of water andfinally stirred into a prealcohol and the remainder of the water.

Example 3 This example shows the preparation of a specific anti-offsetsolution by mixing boric acid, alkali, sorbitol, gum karaya and alcohol.An open mixing tank was provided with heating and cooling coils forassisting the dissolving of the ingredients, a thermometer and agitatingmeans. In this tank 530 lbs. of water containing 30 grams of sodiumhydroxide were heated to 50 C. With vigorous agitation a slurry of 510grams of gum karaya in one liter of alcohol was added slowly. Agitationwas continued for two hours, the temperature being maintained betweenabout 45 and 50 C. The following ingredients were then added insuccession and without artificial heating:

- Pounds Caustic soda solution (49.6% NaOH) 30 Boric acid h 40 Causticsoda solution (49.6% NaOI-I) 20 Sorbitol syrup (84.6% solids) -13? wasstirred for 9 hours and then made an excellent anti-onset composition.

It'should again be pointed out that the concentrations at which thesesolutions are employed are not critical. The solution shown in Example 1has been used for spray purposes with solids contents of from 25 to 50%.At the-upper ranges of concentration the spray becomes syrupy anduneeonomical to use. At lower ranges when spraying the spray guns mustbe opened-too wide and the amount of spray floating in the air becomesobjectionable in the press room. Hence the middle concentrations aresomewhat more satisfactory, though spray gun openings and otheroperational technique will compensate tor wide ranges 02- concentration.

What is claimed is:

1. An anti-offset composition which comprises an aqueous solution oi acombinatlon'oi a soluble organic compound selected fromthe groupconsisting of glycerol, erythritol, pentitols, pen- 'claim 1 in whichthe organic compound is a hexose.

5. An anti-ofl'set composition according to claim 1 in which the organiccompound is a hexitol and the alkali is present in proportions of aboutto 1 equivalent of alkali to each atomic weight of boron.

6. An anti-onset composition according to claim 1 which also contains afurther solvent which increases the volatility oi the solution.

fl. An anti-oflset composition according to claim 1 which also containsa gelatinizing agent. a. A composition according to claim 1 in which theorganic compound is a hexitol, and the solution also contains a furthersolvent which increases its volatility and a gelatinizing agent.

9. A composition according to claim 1 in which the organic compound isglycerol, and the solution also contains a further solvent'which'increases its volatility and a gelatinizing agent.

10. A composition according to claim 1 in which the organic compound isa hexose, and the solution also contains a further solvent whichincreases its volatility and a gelatinizing agent.

11. An anti-offset composition which comprises an aqueous solution of acombination of a hexitol, a boric acid producing material, a smaproportion of locust bean gum, and a water-miscible alcohol, saidcomposition forming resinous material on drying.

5 13. A process of preventing oifset from inked surfaces which comprisesspraying onto the inked suriacea composition which comprises an aqu'eous solution of a combination of a hexitol, a boric acid producingmaterial, and an alkali, the spray 1o distance, size, and quantity beingso adjusted thatanti-offsetting lands are produced upon the inkedsurface. l

4 14. A process according to claim 13 in which the inked surface isheated prior to spraying.

15 15. A process according to claim 13 in which the combination alsocontains a. water-miscible alcohol and gum karaya,

. ERNEST G. ALMY CERTIFICATE CORRECTION. Patent No. 25551;,979. August1, 191411..

ERNEST G. ALHY. 1

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction as follows: I Page 1,first column, line 60,- for "ad" reed--and--; page 2, first column, line6h, for "most" read --more--; and that the said Letters Patent should beread with 'this correction therein that the same may confom tothe'record of the case in the Patent Office, I

Signed and sealed this 5th day of September, A. D. 191m.

Leslie Frazer Acting Commissioner of Patents.

